Continuously variable transmission

ABSTRACT

A continuously variable transmission including: a pair of pressing means that form a torque transmission contact portion in a disk overlapping area where the input disk and the output disk are overlapped; target slip rate setting means that is configured to set a target slip rate between the input disk and the output disk in the torque transmission contact portion to a value higher than a torque transmission start slip rate in the torque transmission contact portion; and control means that is configured to control a force for clamping and pressing both the disks using the pressing means such that an actual slip rate in the torque transmission contact portion becomes the target slip rate.

TECHNICAL FIELD

The present invention relates to a continuously variable transmission.

BACKGROUND ART

In the related art, a transmission unit was discussed in JP 2010-53995A, in which a disk overlapping area where a part of an input disk and apart of an output disk are overlapped with each other is provided, andthe input disk and the output disk are clamped between a pair ofpressing rollers to make contact with each other in the disk overlappingarea.

SUMMARY OF INVENTION

In the transmission unit of the aforementioned technique, a torquetransmission contact portion is formed between the pressing roller andthe disk by elastically deforming the disk using the pressing roller.

In the transmission unit, rotation transmitted from the motor to theinput shaft is transmitted from the input disk to the output disk usinga torque transmission contact portion. In the torque transmissioncontact portion, the circumferential speed of the output disk increasesdue to a frictional force in an area where the circumferential speed ofthe input disk is faster than the circumferential speed of the outputdisk. Meanwhile, since the frictional force in the area where thecircumferential speed of the output disk is faster than thecircumferential speed of the input disk in the torque transmissioncontact portion is exerted to decelerate the output disk, it isdesirable to reduce such an area.

However, in the aforementioned technique, such a requirement is notconsidered, and the torque transmission rate is degradeddisadvantageously.

It is therefore an object of this disclosure to improve the torquetransmission rate in the continuously variable transmission.

According to an aspect of this disclosure, there is provided acontinuously variable transmission including: an input shaft connectedto a motor and supported by a transmission unit casing member; an outputshaft arranged in parallel with the input shaft and supported by thetransmission unit casing member; a discoidal input disk that is providedin the input shaft and has an outer circumferential edge arranged closeto the output shaft; a discoidal output disk that is provided in theoutput shaft and has an outer circumferential edge arranged close to theinput shaft; a pair of pressing means provided movably along a shaftcenter connecting line obtained by connecting a shaft center of theinput shaft and a shaft center of the output shaft in a disk overlappingarea where the input disk and the output disk are overlapped, so that atorque transmission contact portion is formed by clamping and pressingboth the disks in a position corresponding to a target shift ratio toelastically deform both the disks; target slip rate setting means thatis configured to set a target slip rate between the input disk and theoutput disk in the torque transmission contact portion to a value higherthan a torque transmission start slip rate in the torque transmissioncontact portion; and control means that is configured to control a forcefor clamping and pressing both the disks using the pressing means suchthat an actual slip rate in the torque transmission contact portionbecomes the target slip rate.

In this configuration, it is possible to increase an area where a torquecan be transmitted from the input disk to the output disk in the torquetransmission contact portion by generating slippage between the inputdisk and the output disk. Therefore, it is possible to improve thetorque transmission rate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating the entire configuration of avehicle automatic transmission system;

FIG. 2 is a diagram illustrating a transmission unit as seen from anengine side;

FIG. 3 is a bottom view of FIG. 2;

FIG. 4A is a cross-sectional view taken along a line IV-IV of FIG. 2;

FIG. 4B is an enlarged view illustrating a vicinity of a contact areabetween a pressing roller and a side disk;

FIG. 5A is a schematic diagram illustrating a vicinity of the input diskand the output disk of FIG. 4A;

FIG. 5B is a schematic diagram illustrating a vicinity of the input diskand the output disk of FIG. 4A;

FIG. 6A is a cross-sectional view taken along a line VI-VI of FIG. 2;

FIG. 6B is an enlarged view illustrating a vicinity of an end of apressing roller shaft;

FIG. 7 is a schematic diagram illustrating a cross section taken along aline VII-VII of FIG. 6;

FIG. 8 is a schematic diagram illustrating a relationship between abiasing portion, a holding portion, and a pressing roller;

FIG. 9A is a cross-sectional view taken along a line IX-IX of FIG. 2;

FIG. 9B is a schematic diagram illustrating a cross section taken alonga line X-X of FIG. 9A;

FIG. 10A is a diagram illustrating a relationship between a position ofa second roller follower and a clamping force for clamping a pair ofpressing roller mechanisms;

FIG. 10B is a diagram illustrating a relationship between a position ofthe second roller follower and a clamping force for clamping a pair ofpressing roller mechanisms;

FIG. 11 is a map expressing a relationship between a turning angle and aclamping force of a clamp arm;

FIG. 12A is a diagram for describing a motion of the pressing roller;

FIG. 12B is a diagram for describing a motion of the pressing roller;

FIG. 13A is a diagram illustrating a motion of the pressing roller whena shift ratio is changed from a low side to a high side;

FIG. 13B is a diagram illustrating a motion of the pressing roller whenthe shift ratio is changed from a low side to a high side;

FIG. 13C is a diagram illustrating a motion of the pressing roller whenthe shift ratio is changed from a low side to a high side;

FIG. 14 is a schematic diagram illustrating a state that the pressingroller is inclined to the output shaft side;

FIG. 15 is a flowchart illustrating a control of the shift ratio;

FIG. 16 is a flowchart illustrating a thrust force control using a pairof pressing rollers;

FIG. 17 is a flowchart illustrating a target slip rate computationcontrol;

FIG. 18 is a map expressing a relationship between a fluid temperature,target shift ratio, and a target slip rate;

FIG. 19 illustrates a relationship between a slip rate and torquetransmission rate from the input shaft to the output shaft; and

FIG. 20 is a flowchart illustrating a slip rate computation control.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of this disclosure will be described withreference to the accompanying drawing.

FIG. 1 is a schematic diagram illustrating the entire configuration of avehicle automatic transmission system having a multi-disk continuouslyvariable transmission unit according to this disclosure.

The vehicle automatic transmission system 1 includes an engine 2; amulti-disk continuously variable transmission unit (hereinafter,referred to as a “transmission unit”) 3, left and right driving shafts 4and 5, left and right driving wheels 6 and 7, and a control unit(hereinafter, referred to as a “ATCU”) 8.

The transmission unit 3 includes a transmission unit casing 9, an inputshaft 10, a primary disk 11, a secondary disk 12, a pressing mechanism13, an output shaft 14, a dry starter clutch 15 known in the art, areverse gear 16, a reverse idler gear 17, an output gear 18, asynchronization mechanism 19, a final gear 20, and a differential gearunit 21.

The vehicle automatic transmission system 1 has a three-shaftconfiguration including the input shaft 10, the output shaft 14, and thedriving shafts 4 and 5.

The input shaft 10 and the output shaft 14 are arranged in parallel witha shaft center of the input shaft 10 and a shaft center of the outputshaft 14. The input shaft 10 and the output shaft 14 are rotatablysupported by the transmission unit casing 9.

The transmission unit 3 will be described in detail with reference toFIGS. 2 and 3. FIG. 2 is a diagram illustrating the transmission unit 3as seen from the engine side 2. FIG. 3 is a bottom view of FIG. 2. FIG.4A is a cross-sectional view taken along a line IV-IV of FIG. 2. It isnoted that a part of elements are omitted intentionally in the drawingssubsequent to FIG. 2 for convenient description purposes.

The primary disk 11 is configured by arranging a pair of circular disks11 a along an axial direction of the input shaft 10 and installing themin the input shaft 10 as illustrated in FIGS. 5A and 5B such that theyare rotated in synchronization with the input shaft 10. FIG. 5 is aschematic diagram illustrating vicinities of the input shaft 10 and theoutput shaft 14 of FIG. 4A. A spacer 22 is provided between the pair ofdisks 11 a, and the pair of disks 11 a are arranged with a predeterminedinterval using the spacer 22 in the axial direction of the input shaft10. The primary disk 11 is arranged such that an outer circumferentialedge of the disk 11 a is close to the output shaft 14. The primary disk11 is rotated in the arrow direction of FIG. 2 along with the inputshaft 10.

The secondary disk 12 has a center disk 12 a and a pair of side disks 12b arranged in both sides of the central disk 12 a to face each other.The secondary disk 12 is configured by arranging the center disk 12 aand the side disks 12 b along the axial direction of the output shaft 14and installing them in the output shaft 14 as illustrated in FIGS. 5Aand 5B such that they are rotated in synchronization with the outputshaft 14. A spacer 23 is provided between the center disk 12 a and theside disk 12 b, and the center disk 12 a and the side disk 12 b arearranged with a predetermined interval using the spacer 23 in the axialdirection of the output shaft 14. The secondary disk 12 is arranged suchthat the outer circumferential edge of the center disk 12 a and theouter circumferential edge of the side disk 12 b are close to the inputshaft 10.

The center disk 12 a is a circular disk having a larger thickness in anaxial direction of the output shaft 14 than those of the side disk 12 band the disk 11 a of the primary disk 11. In the center disk 12 a, ahollow 12 c is formed in the inner radial side, and a thrust ballbearing 24 is provided in the hollow 12C.

The side disk 12 b is a circular disk and is warped such that a distancefrom the center disk 12 a increases toward an outer radial side. Thedisk 11 a of the primary disk 11 is arranged between the side disk 12 band the center disk 12 a of the secondary disk 12. The primary disk 11and the secondary disk 12 form a disk overlapping area where the disksare partially overlapped between the input shaft 10 and the output shaft14. The center disk 12 a is positioned in the center of the diskoverlapping area in the axial direction of the input shaft 10.

In the disk overlapping area, the outer circumferential edge of theoutput shaft 14 side of the disk 11 a of the primary disk 11 issupported by the thrust ball bearing 24, so that a gap is formed betweenthe disk 11 a of the primary disk 11 and the center disk 12 a while apressing force of the pressing mechanism 13 described below is notapplied. In addition, since the side disk 12 b of the secondary disk 12is warped such that a distance from the center disk 12 a increasestoward the outer circumferential edge side, a gap is formed between thedisk 11 a of the primary disk 11 and the side disk 12 b of the secondarydisk 12. For this reason, in the disk overlapping area, if aclamping/pressing force (hereinafter, referred to as a thrust force) isnot applied to the primary disk 11 and the secondary disk 12 by thepressing mechanism 13, or if the thrust force is weak, the primary disk11 and the secondary disk 12 do not make contact as illustrated in FIG.5A. Meanwhile, as the thrust force caused by the pressing mechanism 13increases, the primary disk 11 and the secondary disk 12 are elasticallydeformed as illustrated in FIG. 5B, and the primary disk 11 andsecondary disk 12 make contact with each other, so that a torquetransmission contact portion is formed. By forming the torquetransmission contact portion between the primary disk 11 and secondarydisk 12, rotation is transmitted from the input shaft 10 to the outputshaft 14.

The pressing mechanism 13 includes a pair of pressing roller mechanisms30, a pair of disk clamp mechanisms 31, a clamping force adjustmentmechanism 32, and a first actuator 33.

The first actuator 33 shifts the pressing roller mechanism 30 along ashaft center connecting line O obtained by connecting a shaft center ofthe input shaft 10 and a shaft center of the output shaft 14. The shaftcenter connecting line O is perpendicular to the shaft center of theinput shaft 10 and the shaft center of the output shaft 14.

The first actuator 33 has an electric motor 34 and a ball screwmechanism 35. The ball screw mechanism 35 includes a screw shaft 36, abracket 37, and a ball (not illustrated).

The screw shaft 36 has one end connected to a rotation shaft of theelectric motor 34 and is rotated in a forward or backward directiondepending on a rotational direction of the rotation shaft of theelectric motor 34. The screw shaft 36 extends in the shaft centerconnecting line O direction. A plurality of balls (not illustrated) areprovided rollably between the screw shaft 36 and the bracket 37.

As the screw shaft 36 rotates, the bracket 37 moves along the axialdirection of the screw shaft 36, that is, the shaft center connectingline O direction in response to the rotation of the screw shaft 36. Inthe bracket 37, a tapered surface 37 a is formed on the surface of theengine 2 side such that the distance from the screw shaft 36 is reducedtoward the electric motor 34 side. As the bracket 37 reciprocates by theelectric motor 34, a pushrod (not illustrated) such as a cam followerthat follows the tapered surface 37 a reciprocates on the taperedsurface 37 a, so that a release lever of the dry starter clutch 15 isdriven by the pushrod to perform a clutch lock/unlock operation.

The bracket 37 is connected to a second support portion 44 of thepressing roller mechanism 30 and a roller follower support block 48described below in detail through a first shaft 38 extending in theshaft center connecting line O direction. As the screw shaft 36 isrotated by the electric motor 34, the bracket 37 moves forward orbackward along the shaft center connecting line O depending on arotational direction of the screw shaft 36, and the pressing rollermechanism 30 moves forward or backward along the shaft center connectingline O in synchronization with the bracket 37 and the first shaft 38.

A description will now be made for the pressing roller mechanism 30 withreference to FIGS. 6A and 6B. FIG. 6A is a cross-sectional view takenalong the line VI-VI of FIG. 2. FIG. 6B is an enlarged view illustratinga vicinity of an end 42 b of the pressing roller shaft 42.

The pressing roller mechanism 30 includes a pressing roller 40, aholding portion 41, a pressing roller shaft 42, a first support portion43, a second support portion 44, a biasing portion 45, a support block46, and a first roller follower 47.

A pair of pressing roller mechanisms 30 are arranged symmetrically withrespect to the center disk 12 a of the secondary disk 12 and isinstalled in the guide block 49 in an upper side. The guide block 49 isprovided between a pair of guide shaft blocks 50 installed in thetransmission unit casing 9 and is slidably supported by a pair of theguide shafts 51 extending in the shaft center connecting line Odirection. That is, a pair of pressing roller mechanisms 30 are slidablysupported by the guide shaft 51 using the guide block 49 and move in theshaft center connecting line O direction by the first actuator 33, sothat the torque transmission contact portion is formed in a positioncorresponding to the target shift ratio.

The pressing roller shaft 42 extends to intersect with the shaft centerconnecting line O direction and has one end 42 a supported by the firstsupport portion 43 and the other end 42 b supported by the secondsupport portion 44. In the pressing roller shaft 42, the end 42 bsupported by the second support portion 44 has a spherical shape. Theholding portion 41 that supports the pressing roller 40 between thefirst support portion 43 and the second support portion 44 is installedin the pressing roller shaft 42.

The first support portion 43 is provided in a downstream side from thepressing roller 40 in the rotational direction of the primary disk 11and is pivotably supported by the guide block 49 using a pivot shaft 52provided in parallel with the guide shaft 51. The first support portion43 supports one end 42 a of the pressing roller shaft 42 using a needlebearing 53.

The second support portion 44 is provided in an upstream side from thepressing roller 40 in the rotational direction of the primary disk 11and supports the other end 42 b of the pressing roller shaft 42 usingthe support block 46 and the needle bearing 54. A bushing 55 having aspherical leading edge 55 a is provided between the second supportportion 44 and the support block 46 in the axial direction of the inputshaft 10 so that a gap is formed between the second support portion 44and the support block 46. The gap in the axial direction of the inputshaft 10 is positioned in the primary disk 11 side from the bushing 55,and the leading edge 55 a of the bushing 55 abuts on the support block46. The second support portion 44 is connected to an end of the secondshaft 56 where the first roller follower 47 is installed, and the secondshaft 56 extends in a direction perpendicular to the shaft centerconnecting line O direction and the shaft center connecting line Odirection and the axial direction of the input shaft 10. The secondsupport portion 44 moves in the axial direction of the input shaft 10 byvirtue of the clamping force applied to the first roller follower 47. Inresponse to movement of the second support portion 44 to the axialdirection of the input shaft 10, the holding portion 41 that supportsthe first support portion 43, the pressing roller shaft 42, and thepressing roller 40 is pivoted with respect to the shaft center of thepivot shaft 52.

The first support portion 43 is provided to form a gap between theneedle bearing 53 and the pressing roller shaft 42 in the shaft centerconnecting line O direction as illustrated in FIG. 7. FIG. 7 is aschematic diagram taken along the line VII-VII of FIG. 6A. The end 42 dof the pressing roller shaft 42 supported by the second support portion44 has the spherical shape and abuts on the needle bearing 54. Thepressing roller shaft 42 is supported by the first and second supportportions 43 and 44 tiltably with respect to the shaft center connectingline O.

The pressing roller shaft 42 is pivotably supported by the first supportportion 43 using the needle bearing 53 and by the second support portion44 using the needle bearing 54.

The holding portion 41 is provided between the first and second supportportions 43 and 44 and is installed in the pressing roller shaft 42. Theholding portion 41 is pivoted and tilted in synchronization with thepressing roller shaft 42. The holding portion 41 is fixed to the firstshaft portion 57 that rotatably supports the pressing roller 40. Whenthe pressing roller shaft 42 is located perpendicularly to the shaftcenter connecting line O as seen from the axial direction of the inputshaft 10, the shaft center of the first shaft portion 57 matches theshaft center connecting line O. In addition, the first shaft portion 57is provided such that the shaft center of the first shaft portion 57 isinclined against a disk plane in FIG. 4A. A tensile stress is applied tothe holding portion 41 at all times by virtue of a spring 60 of thebiasing portion 45 described below in detail.

The pressing roller 40 is rotatably supported by the first shaft portion57 and is installed in the pressing roller shaft 42 using the holdingportion 41. The pressing roller 40 abuts on the side disk 12 b of thesecondary disk 12 in the disk overlapping area and rotates with respectto the shaft center of the first shaft portion 57 by virtue of africtional force with the side disk 12 b of the secondary disk 12. Apair of pressing rollers 40 clamp and press the disks 11 and 12 as theclamping force transmitted through the first roller follower 47increases, so that the disks 11 and 12 are elastically deformed to formthe torque transmission contact portion.

The pressing roller 40 is supported by the holding portion 41 andreceives a tensile stress from the spring 60 of the biasing portion 45described below in detail at all times together with the holding portion41. For this reason, an inclination of the pressing roller 40 to theoutput shaft 14 side changes depending on the tensile stress from thespring 60 of the biasing portion 45 and the reactive force from thedisks 11 and 12.

An abutting portion 40 a of the pressing roller 40 abutting on thesecondary disk 12 in FIG. 4A is formed by curved surfaces havingdifferent curvatures. The abutting portion 40 a is formed such that itscurvature is reduced toward the leading edge side in the shaft center ofthe pressing roller 40, and a curved surface having a larger curvatureabuts on the secondary disk 12 as the pressing roller 40 is inclinedtoward the output shaft 14 side. Here, if the pressing roller 40 isfurther inclined toward the output shaft 14 side, this state will bereferred to as “an inclination angle is larger.”

Specifically, the curvature of the curved surface of the abuttingportion 40 a becomes 1/34, 1/55, and 1/100 toward the leading edge sideas illustrated in FIG. 4B. In FIG. 4B, a curved surface having acurvature of 1/34 is denoted by a point A, a curved surface having acurvature of 1/55 is denoted by a point B, and a curved surface having acurvature of 1/100 is denoted by a point C. For this reason, as theinclination angle increases, the curvature of the abutting portion 40 aabutting on the secondary disk 12 sequentially changes from “ 1/100,” to“ 1/55,” and to “ 1/34.”

As the inclination angle increases, the curvature of the curved surfacein the contact region increases. Therefore, an area of the contactregion is reduced to a circle-like shape. It is noted that, as theinclination angle increases in this manner, the area of the torquetransmission contact portion is reduced to a circle-like shape.

As illustrated in FIG. 8, the biasing portion 45 has a spring 60 and afixing portion 61. FIG. 8 is a schematic diagram illustrating arelationship between the biasing portion 45, the holding portion 41, andthe pressing roller 40.

One end of the spring 60 is connected to the holding portion 41 in thedisk 11 or 12 side, and the other end is connected to the fixing portion61. The fixing portion 61 is fixed to the first or second supportportion 43 or 44 and moves in the shaft center connecting line Odirection together with the pressing roller 40.

The biasing portion 45 applies a tensile force for pulling the holdingportion 41 and the pressing roller 40 to the input shaft 10 side towardthe holding portion 41 and the pressing roller 40 at all times. As aresult, a force is applied to the holding portion 41 and the pressingroller 40 in a rotational direction with respect to the shaft center ofthe pressing roller shaft 42, so that the holding portion 41 and thepressing roller 40 are generally inclined to the output shaft 14 side.

When the thrust force of the pressing roller 40 is weak, the biasingportion 45 abuts on a pulling stopper (not illustrated) that restrictspivoting of the pressing roller 40 and the holding portion 41 to theinput shaft 10 side. Even in this state, the stopper is provided suchthat a contact region between the abutting portion 40 a of the pressingroller 40 and the side disk 12 b is positioned in the output shaft 14side relative to a perpendicular line drawn from the shaft center of thepressing roller shaft 42 to the side disk 12 b. For this reason, whenthe primary disk 11 and the secondary disk 12 are clamped and pressed bya pair of pressing rollers 40, a second moment opposite to the firstmoment generated by the spring 60 is generated in the pressing roller 40and the holding portion 41 by virtue of the reactive force received bythe pressing roller 40 from the primary disk 11 and the secondary disk12.

As the thrust force of the pressing roller 40 increases, the secondmoment increases, and the pressing roller 40 and the holding portion 41are rotated with respect to the shaft center of the pressing rollershaft 42, so that the inclination angle is reduced. In addition, thepressing roller 40 and the holding portion 41 are held in a positionwhere the first and second moments are balanced. As the inclinationangle decreases, the curvature of the abutting portion 40 a of thepressing roller 40 abutting on the side disk 12 b decreases, and the acontact area between the pressing roller 40 and the side disk 12 bincreases. That is, as the thrust force of the pressing roller 40increases, the contact area between the pressing roller 40 and the sidedisk 12 b and the area of the torque transmission contact portionincrease. As a result, it is possible to suppress an increase of thepressure per unit area in the contact region and the torque transmissioncontact portion even when the thrust force of the pressing roller 40increases.

As illustrated in FIG. 6A, the second shaft 56 connected to the secondsupport portion 44 is inserted into the inner circumferential hole 47 aand abuts on the side surfaces 67 a and 68 a of the disks 11 and 12 sideof the clamp arm 66 described below, so that the first roller follower47 is rolled. If the transmission unit 3 is seen from the engine 2 side,a position of the first roller follower 47 approximately matches aposition of the torque transmission contact portion formed by a pair ofpressing rollers 40 as seen in the extending direction of the pressingroller shaft 42.

An end of the second shaft 56 opposite to the end connected to thesecond support portion 44 is inserted into a hole 48 a formed in theroller follower support block 48. The hole 48 a is an elliptical holeformed along the axial line of the input shaft 10. The roller followersupport block 48 supports the second shaft 56 along the hole 48 a suchthat the second shaft 56 can slide along the axial line of the inputshaft 10. In addition, the roller follower support block 48 is connectedto the bracket 37 through the first shaft 38 extending in the shaftcenter connecting line O direction and moves in the shaft centerconnecting line O direction depending on movement of the bracket 37.

The disk clamp mechanism 31 includes an arm shaft 65 and a clamp arm 66.

The arm shaft 65 is a circular columnar member extending perpendicularlyto the shaft center connecting line O and the input shaft 10. The armshaft 65 is provided to have a shaft center perpendicular to the shaftcenter of the input shaft 10 and overlap with the center of the primarydisk 11 in the axial direction of the input shaft 10 as illustrated inFIG. 6A.

The clamp arm 66 is a pair of arms including a front clamp arm 67 and arear clamp arm 68.

The front clamp arm 67 is a plate-like member having an approximatelyL-shape as illustrated in FIG. 3. One end side of the front clamp arm 67is pivotably supported by the arm shaft 65. In the other end of thefront clamp arm 67, an engagement portion 72 of the clamping forceadjustment mechanism 32 described below is formed. A side surface 67 aof the front clamp arm 67 in the disk 11 or 12 side (a surface forming athickness of the plate-like member) abuts on the first roller follower47 as illustrated in FIG. 6A.

The rear clamp arm 68 is a plate-like member having an approximatelyL-shape as illustrated in FIG. 3. One end side of the rear clamp arm 68is pivotably supported by the arm shaft 65. The other end of the rearclamp arm 68 is connected to the casing 70 of the clamping forceadjustment mechanism 32 described below. A side surface 68 a of the rearclamp arm 68 in the disk 11 or 12 side (a surface forming a thickness ofthe plate-like member) abuts on the first roller follower 47 asillustrated in FIG. 6A.

Each of the front and rear clamp arms 67 and 68 is pivotably supportedby the arm shaft 65, and the clamp arm 66 is pivoted by using the armshaft 65 as a fulcrum by virtue of the clamping force generated by theclamping force adjustment mechanism 32, so that the clamping force ofthe disks 11 and 12 is adjusted by driving a pair of pressing rollermechanisms 30.

The clamping force adjustment mechanism 32 includes a casing 70, asecond shaft portion 71, an engagement portion 72, a pivot portion 73, acompression spring 74, and a second actuator (not illustrated).

The casing 70 is connected to an end of the rear clamp arm 68. Thecasing 70 houses a part of the pivot portion 73 and is installed withthe second shaft portion 71.

The second shaft portion 71 is a circular columnar member having a shaftcenter in parallel with the shaft center of the arm shaft 65. The secondshaft portion 71 is installed in the casing 70 so as to pivotablysupport the pivot portion 73 with respect to the shaft center connectingline O. A gap is provided between the second shaft portion 71 and thecasing 70. This gap absorbs influence of a dimensional tolerance, acomponent variation, and the like. Therefore, it is possible to clamp apair of pressing roller mechanisms 30 using the clamp arm 66 withexcellent balance.

The engagement portion 72 has a connecting portion 75 that is formed inan end of the front clamp arm 67 and extends to the rear clamp arm 68side from this end, and a curved portion 76 that extends from the end ofthe connecting portion 75 of the rear clamp arm 68 side to enclose thesecond shaft portion 71. The curved portion 76 has an outercircumferential wall having an arc shape centered at the shaft center ofthe second shaft portion 71. The second roller follower 79 of the pivotportion 73 makes contact with the outer circumferential wall of thecurved portion 76 and rolls thereon.

As illustrated in FIGS. 9A and 9B, the pivot portion 73 has a pivotingbody 77, a rotation transmitting block 78, and a second roller follower79. The pivoting body 77 has a first body 80 and a second body 81. FIG.9A is a cross-sectional view taken along the line IX-IX of FIG. 2. FIG.9B is a schematic diagram illustrating the cross section X-X of FIG. 9A.

The first body 80 is configured by connecting one-side ends of a pair offirst plate-like members 80 a extending by interposing the second shaftportion 71 through a first bending portion 80 b and has an approximatelyU-shape with the second shaft portion 71 being interposed. The firstplate-like member 80 a abuts on the outer circumferential wall of thesecond shaft portion 71 and is supported pivotably by the second shaftportion 71 and slidably along the extending direction of the firstplate-like member 80 a. The first body 80 has a stopper 82 that supportsone end of the compressing spring 74 in the end opposite to the firstbending portion 80 b.

The rotation transmitting block 78 where the second shaft portion 71penetrates is pivotably supported by the second shaft portion 71. Therotation transmitting block 78 supports the other end of the compressionspring 74 opposite to the end supported by the stopper 82.

As illustrated in FIG. 9B, the second body 81 is configured byconnecting one-side ends of a pair of second plate-like members 81 aextending perpendicularly to a coaxial direction to interpose the curvedportion 76 in the axial direction of the second shaft portion 71 to eachother using a second bending portion 81 b and has an approximatelyU-shape. The second bending portion 81 b perpendicularly adjoins thefirst bending portion 80 b of the first body 80. The second bendingportion 81 b abuts on the rotation transmitting block 78 so as to serveas a stopper for preventing the pivoting body 77 from moving in adirection from the second shaft portion 71 toward the compression spring74. A third shaft 83 for pivoting the pivot portion 73 using a secondactuator (not illustrated) penetrates through the second plate-likemember 81 a. As the third shaft 83 is pivoted, the pivoting body 77 ispivoted with respect to the shaft center of the second shaft portion 71in synchronization with the second roller follower 79.

[Description of Operation of Thrust Force Adjustment Mechanism]

One end of the compression spring 74 is supported by the rotationtransmitting block 78, and the other end is supported by the stopper 82of the first body 80. The rotation transmitting block 78 is pivotablysupported by the second shaft portion 71 installed in the casing 70. Forthis reason, the pivoting body 77 is biased by a restoring force of thecompression spring 74 toward the stopper 82 from the second shaftportion 71 at all times. However, since the second bending portion 81 bof the second body 81 positioned oppositely to the compression spring 74with respect to the second shaft portion 71 abuts on the rotationtransmitting block 78, movement of the pivoting body 77 from the secondshaft portion 71 to the compression spring 74 is restricted.

The second roller follower 79 is supported by the third shaft 83 engagedwith the inner circumferential hole 79 a and is provided between a pairof the second plate-like members 81 a. The second roller follower 79abuts on the outer circumferential wall of the curved portion 76, havingthe spin loss, and rolls thereon. The second roller follower 79 ispivoted by the second actuator using the third shaft 83 insynchronization with the pivoting body 77 centered at the shaft centerof the second shaft portion 71 and is biased by the compression spring74 toward the second shaft portion 71 at all times.

The clamping force adjustment mechanism 32 having the aforementionedconfiguration changes a direction of the force that biases the secondroller follower 79 to the second shaft portion 71 using the compressionspring 74 by pivoting the second roller follower 79 with respect to theshaft center of the second shaft portion 71. As a result, a force thatpresses the front clamp arm 67 toward the rear clamp arm 68 side, thatis, the clamping force for clamping a pair of pressing roller mechanisms30 is changed.

Here, a relationship between the position of the second roller follower79 and the clamping force for clamping a pair of pressing rollermechanisms 30 will be described with reference to FIGS. 10A and 10B.FIGS. 10A and 10B are diagrams illustrating a relationship between theposition of the second roller follower 79 and the clamping force forclamping a pair of pressing roller mechanisms 30.

In the area where the second roller follower 79 is far from theconnecting portion 75, when a direction of the force that biases thesecond roller follower 79 toward the second shaft portion 71 using thecompression spring 74 is in parallel with the shaft center connectingline O as illustrated in FIG. 10A, the force that presses the frontclamp arm 67 to the rear clamp arm 68 side using the second rollerfollower 79, that is, the clamping force for clamping a pair of pressingroller mechanisms 30 using the clamp arm 66 also becomes insignificantor zero. In the following description, this state will be referred to asa “reference position” of the pivot portion 73, and an angle of thesecond roller follower 79 pivoting from the reference position will bereferred to as a “turning angle.” In addition, if the second rollerfollower 79 is further pivoted toward the connecting portion 75 side,this state will be referred to as “the turning angle of the secondroller follower 79 is large.”

As the turning angle of the second roller follower 79 increases, adirection of the force that biases the second roller follower 79 towardthe second shaft portion 71 by the compression spring 74 is changed, sothat the force that presses the front clamp arm 67 to the rear clamp arm68 side using the second roller follower 79 increases, and the clampingforce for clamping a pair of pressing roller mechanisms 30 using theclamp arm 66 increases.

As illustrated in FIG. 10B, as the second roller follower 79 makescontact with the connecting portion 75, the clamping force for clampinga pair of pressing roller mechanisms 30 using the clamp arm 66 ismaximized. Here, a relationship between the turning angle and theclamping force caused by the clamp arm 66 is expressed in FIG. 11. Asthe turning angle increases, the clamping force increases. However, itis recognized that, if the turning angle increases over a predeterminedvalue, an increase amount of the clamping force relative to an increaseamount of the turning angle is reduced. For this reason, according tothis embodiment, a maximum turning angle of the second roller follower79 is set to a predetermined turning value in FIG. 11. A turning angleat which the second roller follower 79 makes contact with the connectingportion 75 becomes the maximum turning angle, and the connecting portion75 serves as a stopper for restricting pivoting of the second rollerfollower 79.

As illustrated in FIG. 1, the ATCU 8 receives a signal from a motorrotation sensor 100 that detects an operation amount of the screw shaft36 using the first actuator 33, a signal from a first rotation speedsensor 101 that detects a rotation speed of the input shaft 10 of thetransmission unit 3, a signal from a second rotation speed sensor 102that detects a rotation speed of the output shaft 14 of the transmissionunit 3, a signal from an oil temperature sensor 103 that detects atemperature of a lubricant supplied to the transmission unit 3, a signalfrom an angle sensor 104 that detects a turning angle of the secondroller follower 79, a signal from an accelerator opening level sensor105 that detects an accelerator opening level, a signal from aninhibitor switch 106 that detects a position of the selector, and asignal relating to the input torque from an ECU (not illustrated) thatcontrols the engine 2.

The ATCU 8 controls the electric motor 34 and the second actuator of theclamping force adjustment mechanism 32 based on the received signals.The ATCU 8 includes a central processing unit (CPU), a read-only memory(ROM), a random-access memory (ROM), and the like. As the CPU reads aprogram stored in the RAM, a function of the ATCU 8 is operated.

[Reverse Mechanism]

When the selector is manipulated to an R-position to drive a vehiclebackward, first, formation of the torque transmission contact portion isprevented by reducing the clamping force of the clamping forceadjustment mechanism 32 and the thrust force of the pressing roller 40.As a result, transmission of a torque from the primary disk 11 to thesecondary disk 12 is blocked. In addition, the reverse gear 16 and theinput shaft 10 are engaged with each other by moving a coupling sleeve19 a of the synchronization mechanism 19. As a result, rotation of theinput shaft is sequentially transmitted to the synchronization mechanism19, the reverse gear 16, the reverse idler gear 17, and the output shaft14 in this order to drive the vehicle backward.

[Parking Mechanism]

When the selector is manipulated to a P-position to park the vehicle,the reverse gear 16 is engaged with the input shaft 10 by moving thecoupling sleeve 19 a of the synchronization mechanism 19. As a result, arotatable direction of the output shaft 14 becomes opposite to therotational direction at which the torque transmission contact portion isformed by the pressing roller 40. In addition, the primary disk 11 andthe secondary disk 12 are clamped and pressed by a pair of pressingrollers 40 to form the torque transmission contact portion. As a result,a rotational direction of the secondary disk 12 becomes a rotationaldirection at which the torque transmission contact portion is formed bythe pressing roller 40. In this manner, when the selector is manipulatedto the P-position, the reverse gear 16 is locked, the disks 11 and 12are clamped and pressed by the pressing roller 40 to form the torquetransmission contact portion, and the transmission unit 3 isinterlocked. As a result, it is possible to prevent movement of thevehicle.

When the selector is manipulated to the P-position to park the vehicle,the pressing roller mechanism 30 clamps and presses the primary disk 11and the secondary disk 12 in a position where the shift ratio becomesthe lowest level, and the clamping force generated by the clamping forceadjustment mechanism 32 is set to the maximum. As a result, it ispossible to increase a breaking force.

Next, the effects of this embodiment will be described.

[Motion of Pressing Roller 40 when No Shift Operation]

A motion of the pressing roller 40 when the transmission unit 3 does notmake a shift operation will be described with reference to FIGS. 12A and12B.

The end 42 b of the pressing roller shaft 42 in the second supportportion 44 side has the spherical shape and is supported by the secondsupport portion 44 using the needle bearing 54 and the support block 46.In addition, the end 42 a of the pressing roller shaft 42 in the firstsupport portion 43 side is supported by the first support portion 43using the needle bearing 53 by providing a predetermined gap in theshaft center connecting line O direction. In this manner, the pressingroller shaft 42 and the pressing roller 40 are supported by the firstsupport portion 43 and the second support portion 44 tiltably in theshaft center connecting line O direction.

Typically, when the pressing roller mechanism 30 is held at a certainposition in the disk overlapping area, that is, the vehicle is not inthe shift operation, the shaft center of the first shaft portion 57 thatrotatably supports the pressing roller 40 matches the shaft centerconnecting line O as illustrated in FIG. 12A. However, since thepressing roller shaft 42 is tiltably supported by the first and secondsupport portions 43 and 44, the shaft center of the first shaft portion57 may be inclined to the shaft center connecting line O as illustratedin FIG. 12B. If this state is maintained, a load applied to the pressingroller mechanism 30 increases, so that the pressing roller mechanism 30may be deteriorated.

In the state of FIG. 12B, a frictional force is generated between thepressing roller 40 and secondary disk 12 as indicated by the solid arrowwhich is a tangential direction of the secondary disk 12. The frictionalforce indicated by the solid arrow can be decomposed into forcecomponents indicated by dotted arrows perpendicular to the axial line ofthe pressing roller 40. The force component indicated by the dottedarrow A rotates the pressing roller 40, and the force componentindicated by the dotted arrow B generates a moment in the pressingroller 40, so that the pressing roller 40 is forced to return to itsoriginal position. In this manner, when the shaft center serving as arotation center of the pressing roller 40 is inclined against the shaftcenter connecting line O, a force for returning to its original positionis generated in the pressing roller 40, and the pressing roller 40 movestogether with the pressing roller shaft 42 such that the shaft centermatches the shaft center connecting line O. Therefore, the pressingroller 40 automatically returns to the state of FIG. 12A in which theshaft center matches the shaft center connecting line O.

[Motion of Pressing Roller 40 in Shift Operation]

A description will now be made for a motion of the pressing roller 40when a shift operation is performed using the transmission unit 3.

The transmission unit 3 implements a continuous speed variation forcontinuously changing a shift ratio by moving a pair of pressing rollers40 along the shaft center connecting line O to change a formation placeof the torque transmission contact portion in the disk overlapping area.

When the pressing roller 40 is positioned in the input shaft 10 side, adistance from the input shaft 10 to the torque transmission contactportion is short, and a distance from the output shaft 14 to the torquetransmission contact portion is long. For this reason, a rotation speedof the secondary disk 12 becomes slower than the rotation speed of theprimary disk 11, and the shift ratio increases. As the pressing roller40 moves to the output shaft 14 side, the distance from the input shaft10 to the torque transmission contact portion is lengthened, and thedistance from the output shaft 14 to the torque transmission contactportion is shortened. For this reason, the rotation speed of thesecondary disk 12 becomes fast relative to the rotation speed of theprimary disk 11, and the shift ratio decreases. In this manner, as apair of pressing rollers 40 move from the input shaft 10 side to theoutput shaft 14 side along the shaft center connecting line O, the shiftratio changes from LOW (high shift ratio) to HIGH (low shift ratio).

The shift operation is performed by moving the second support portion 44in the shaft center connecting line O direction using the first actuator33. Movement of the second support portion 44 is transmitted through thepressing roller shaft 42, and the pressing roller 40 and the firstsupport portion 43 move in the shaft center connecting line O directionto follow the second support portion 44 as the second support portion 44moves. The second support portion 44 is located in the upstream sidefrom the pressing roller 40 in the rotational direction of the primarydisk 11, and the first support portion 43 is located in the downstreamside from the pressing roller 40 in the rotational direction of theprimary disk 11.

A description will now be made for a case where the shift ratio changesto the HIGH side with reference to FIGS. 13A, 13B, and 13C.

If the second support portion 44 moves to the output shaft 14 side usingthe first actuator 33 as illustrated in FIG. 13B from the state that theshift ratio of the transmission unit 3 has a certain value (FIG. 13A),first, the pressing roller shaft 42 is inclined by virtue of the effectof the gap provided in the first support portion 43, and a moment isgenerated in the pressing roller 40 accordingly, so that the pressingroller 40 starts movement by virtue of the effect of the moment. Africtional force with the second disk 12 is generated in the pressingroller 40 as indicated by the solid line. The frictional force indicatedby the solid arrow can be decomposed into force components indicated bydotted arrows as the pressing roller 40 is inclined. A moment isgenerated in the pressing roller 40 by virtue of the force indicated bythe dotted arrow B, so that the pressing roller 40 moves to the outputshaft 14 side. That is, as the pressing roller 40 is inclined during theshift operation, a force is generated from the pressing roller 40 itselfto move toward the output shaft 14 side, so that the pressing roller 40moves to the output shaft 14 side to follow movement of the secondsupport portion 44.

As the second support portion 44 moves by the first actuator 33 to aposition corresponding to the target shift ratio, the second supportportion 44 stops. As the second support portion 44 stops, first, thepressing roller shaft 42 is inclined by virtue of the effect of the gapprovided in the first support portion 43 into the state illustrated inFIG. 12B. Accordingly, a moment is generated in the pressing roller 40,and the pressing roller 40 starts to move by virtue of the moment. Then,the shaft center of the first shaft portion 57 that rotatably supportsthe pressing roller 40 matches the shaft center connecting line O, andthe pressing roller 40 is held in a position capable of implementing thetarget shift ratio as illustrated in FIG. 13C.

Similar to a case where the shift ratio changes to the HIGH side, whenthe transmission unit 3 changes the shift ratio to the LOW side, a forceis generated from the pressing roller 40 to follow movement of thesecond support portion 44 as the second support portion 44 moves.

In this manner, when the shift operation is performed by moving thepressing roller mechanism 30, the pressing roller 40 is inclined bymoving the second support portion 44 in the shaft center connecting lineO direction using the first actuator 33, so that a force for moving thepressing roller 40 to the movement direction of the second supportportion 44 is generated from the pressing roller 40 itself. For thisreason, the transmission unit 3 performs the shift operation by applyinga weak force to the second support portion 44 using the first actuator33.

[Thrust Force Under Same Input Torque]

A description will now be made for the thrust force under the same inputtorque.

In the pressing mechanism 13, the shaft center of the arm shaft 65extends perpendicularly to the shaft center connecting line O andintersects with the shaft center of the input shaft 10. In addition, thedisk clamp mechanism 31 is provided in the center of the gap between apair of the primary disks 11. For this reason, when the shaft center ofthe pressing roller shaft 42 is perpendicular to the shaft centerconnecting line O, a distance from the shaft center of the input shaft10 to the torque transmission contact portion, specifically, a distanceto the center of the torque transmission contact portion becomes equalto a distance from the shaft center of the arm shaft 65 to the clampingposition of the first roller follower 47 using the clamp arm 66,specifically, a distance to the line connecting the shaft centers of apair of first roller followers 47.

The disk clamp mechanism 31 clamps the pressing roller mechanism 30 byusing the arm shaft 65 as the fulcrum. When the clamping force of theclamp arm 66 using the clamping force adjustment mechanism 32 isconstant, for example, when the distance from the shaft center of thearm shaft 65 to the first roller follower 47 of the pressing rollermechanism 30 is doubled, the clamping force for clamping a pair pressingroller mechanisms 30, that is, the thrust force of the pressing roller40 becomes a half.

For this reason, for example, when the shift ratio changes such that thedistance from the input shaft 10 to the center of the torquetransmission contact portion is doubled, the distance from the shaftcenter of the arm shaft 65 to the first roller follower 47 is alsodoubled, and the thrust force of the pressing roller 40 becomes a half.In this case, the thrust force under the same input torque of the inputshaft 10 matches the shift ratio.

[Thrust Force Control Using Pressing Mechanism 13]

Next, a description will be made for a thrust force control using thepressing mechanism 13.

The pressing mechanism 13 changes the clamping force for clamping a pairof first roller followers 47 by changing the position of the pressingroller mechanism 30 along the shaft center connecting line O and theturning angle of the second roller follower 79 of the clamping forceadjustment mechanism 32 in order to change the thrust force of thepressing roller 40.

In the center of the torque transmission contact portion formed by apair of pressing roller mechanisms 30, the circumferential speed of theprimary disk 11 is equal to the circumferential speed of the second disk12, and the direction of the position vector is also equal. However, ina position decentered from the center of the torque transmission contactportion, the circumferential speed of the primary disk 11 is differentfrom the circumferential speed of the second disk 12, and the directionof the position vector is also different. For this reason, in the torquetransmission contact portion, the spin loss which is a loss in torquetransmission is generated due to such facts.

The spin loss serving as a loss in torque transmission is also generatedbetween the pressing roller 40 and the side disk 12 b of the secondarydisk 12.

According to this embodiment, the spin loss between the pressing roller40 and the side disk 12 b of the secondary disk 12 is reduced byinclining the pressing roller 40 toward the output shaft 14 side. Inaddition, the spin loss in the torque transmission contact portion isreduced by adjusting the thrust force using the clamping forceadjustment mechanism 32.

Here, a description will be made first for the effect of inclining thepressing roller 40. Then, the effect of adjusting the thrust force usingthe clamping force adjustment mechanism 32 will be described.

[Inclination of Pressing Roller 40]

In order to reduce the spin loss between the pressing roller 40 and theside disk 12 b of the secondary disk 12, the pressing roller 40 isprovided such that a shaft center of the first shaft portion 57 of theholding portion 41 serving as a rotational center of the pressing roller40 is inclined against the shaft center connecting line O.

As shown in FIG. 14, when an extension line from the shaft center of thefirst shaft portion 57 intersects with the rotational center P of theside disk 12 b on the surface of the secondary disk 12, a triangle PAA′is analogous to a triangle PBB′, where “A” denotes a center of thetorque transmission contact portion, “AA′” denotes a radius of rotationof the pressing roller 40 at the center A, “B” denotes an abuttingportion in the output shaft 14 side from the center A, and “BB′” denotesa radius of rotation of the pressing roller 40 in the abutting portionB. As a result, a ratio between PA and PB becomes equal to a ratiobetween AA′ and BB′, the circumferential speed of the secondary disk 12in the center A of the torque transmission contact portion becomes equalto the circumferential speed of the pressing roller 40, and thecircumferential speed of the secondary disk 12 in the abutting portion Bbecomes equal to the circumferential speed of the pressing roller 40. Inthis case, the spin loss between the secondary disk 12 and the pressingroller 40 is not generated. If the line between the abutting portions Aand B is a straight line, the spin loss is not generated. However, ifthe line between the abutting portions A and B has a curved shape havinga different curvature, the spin loss is generated insignificantly.

If the extension line from the shaft center of the first shaft portion57 does not intersect with the point P even when the pressing roller 40is inclined, the spin loss is generated between the secondary disk 12and the pressing roller 40. However, it is possible to reduce the spinloss, compared to a case where the shaft center of the first shaftportion 57 is in parallel with the shaft center connecting line O.

Preferably, the inclination angle of the pressing roller 40 is set suchthat the extension line from the shaft center of the first shaft portion57 intersects with the point P.

[Adjustment of Thrust Force of Clamping Force Adjustment Mechanism 32]

(When the Second Roller Follower 79 is Located in the ReferencePosition)

When the second roller follower 79 is located in the reference position,a direction of the force that biases the second roller follower 79toward the second shaft portion 71 using the compression spring 74becomes in parallel with the shaft center connecting line O, so that aforce that presses the front clamp arm 67 toward the rear clamp arm 68using the clamping force adjustment mechanism 32 becomes insignificantor zero. The clamp arm 66 abuts on the first roller follower 47 of thepressing roller mechanism 30 by the side surfaces 67 a and 68 a of thedisks 11 and 12 side and clamps the first roller follower 47. For thisreason, as the force that presses the front clamp arm 67 toward the rearclamp arm 68 side using the second roller follower 79 becomesinsignificant or zero, the clamping force for clamping the first rollerfollower 47 is also reduced.

The pressing roller mechanism 30 is supported by the guide block 49pivotably with respect to the pivot shaft 52 so as to generate thethrust force by virtue of the clamping force applied to the first rollerfollower 47 by using the pivot shaft 52 as a fulcrum. When the clampingforce for clamping the first roller follower 47 is weak, a force forpivoting the pressing roller mechanism 30 toward the disks 11 and 12side is weak, the torque transmission contact portion is not formed androtation is not transmitted from the input shaft 10 to the output shaft14.

When the second roller follower 79 is located in the reference position,the torque transmission contact portion is not formed. Therefore, it ispossible to easily move the pressing roller mechanism 30 along the shaftcenter connecting line. For this reason, it is possible to easily returnthe pressing roller 40 to a position where the shift ratio becomes thelowest level even when a downshift control is performed, in which thevehicle stops before the shift ratio is at the lowest level, and thepressing roller 40 is forced to move to the position where the shiftratio becomes the lowest level in preparation for the next start.

It is noted that, if the second roller follower 79 is pivoted from thereference position to the side opposite to the connecting portion 75side, that is, such that the turning angle is reduced, a force isapplied such that the front clamp arm 67 is separated from the rearclamp arm 68 by virtue of a force that biases the second roller follower79 toward the second shaft portion 71 using the compression spring 74.In order to reliably prevent formation of the torque transmissioncontact portion, it may be possible to rotate the second roller follower79 from the reference position to the side opposite to the connectingportion 75 side.

It is noted that the first moment is generated by the biasing portion 45to incline the pressing roller 40 to the output shaft 14 side, so thatthe inclination angle of the pressing roller 40 is maintained by thestopper.

(When the Turning Angle of the Second Roller Follower 79 Increases)

When the turning angle of the second roller follower 79 increases, theforce that presses the front clamp arm 67 to the rear clamp arm 68 sideincreases. For this reason, the clamping force for clamping the firstroller follower 47 using the clamp arm 66 increases. The clamp arm 66clamps the first roller follower 47 by using the arm shaft 65 as thefulcrum and using the end opposite to the arm shaft 65 as a point ofeffort, it is possible to clamp the first roller follower 47 with a weakforce.

The curved surface of the curved portion 76 where the second rollerfollower 79 rolls is formed in an arc shape centered at the shaft centerof the second shaft portion 71, and the second roller follower 79 ispivoted with respect to the shaft center of the second shaft portion 71.Therefore, the length of the compression spring 74 is nearly constantregardless of the position of the second roller follower 79. For thisreason, it is possible to change the clamping force for clamping a pairof first roller followers 47 by changing a direction of the force thatbiases the second roller follower 79 toward the second shaft portion 71using the compression spring 74 without significantly changing astrength of the force. Therefore, it is possible to move the secondroller follower 79 with a weak force.

As the clamping force for clamping the first roller follower 47increases, the pressing roller mechanism 30 is pivoted to the disks 11and 12 side with respect to the shaft center of the pivot shaft 52.

As the pressing roller mechanism 30 is pivoted to the disks 11 and 12side with respect to the shaft center of the pivot shaft 52, the sidedisk 12 b of the secondary disk 12 is elastically deformed by thepressing roller 40 toward the center disk 12 a side to cause the sidedisk 12 b and the disk 11 a of the primary disk 11 to make contact witheach other. Furthermore, the pressing roller mechanism 30 elasticallydeforms the disk 11 a of the primary disk 11 to the center disk 12 aside to cause the disk 11 a of the primary disk 11 and the center disk12 a to make contact with each other. As a result, the torquetransmission contact portion is formed so that the rotation istransmitted from the input shaft 10 to the output shaft 14.

The pressing roller mechanism 30 generates the thrust force by using thepivot shaft 52 provided in one end 42 a side of the pressing rollershaft 42 as the fulcrum and using the first roller follower 47 providedin the other end 42 b side of the pressing roller shaft 42 as a point ofeffort. For this reason, it is possible to form the torque transmissioncontact portion by causing the primary disk 11 and the secondary disk 12to make contact with each other with a weak force using a pair ofpressing rollers 40 and transmit rotation from the input shaft 10 to theoutput shaft 14.

As the turning angle of the second roller follower 79 increases, thepressing roller mechanism 30 is further pivoted to the disks 11 and 12side with respect to the shaft center of the pivot shaft 52, so that thethrust force caused by the pressing roller 40 increases.

It is possible to reduce the spin loss in the torque transmissioncontact portion by reducing the area of the torque transmission contactportion and approximating the shape of the torque transmission contactportion to a circular shape. However, if the area of the torquetransmission contact portion is reduced, a pressure per unit area of thetorque transmission contact portion increases when the thrust forcecaused by the pressing roller 40 increases, so that the primary disk 11,the secondary disk 12, or the pressing roller mechanism 13 may bedeteriorated. In this regard, it is possible to suppress deteriorationof the primary disk 11, the secondary disk 12, or the pressing rollermechanism 13 while the spin loss is reduced by adjusting the inclinationangle of the pressing roller 40.

In the pressing roller 40, the first moment is generated by the biasingportion 45. In addition, the pressing roller 40 receives a reactiveforce from the disks 11 and 12, and the second moment opposite to thefirst moment is generated by the reactive force of the disks 11 and 12.The pressing roller 40 is held in a position where the first and secondmoments are balanced. Since the first moment is generated by the biasingportion 45, a strength of the first moment changes depending on thelength of the spring 60. Meanwhile, the strength of the second momentchanges depending on the reactive force received from the disks 11 and12, that is, the thrust force.

When the thrust force is weak, the second moment is weak. Therefore, thepressing roller 40 of the disks 11 and 12 side is pulled to the inputshaft 10 side by the biasing portion 45, so that the inclination angleof the pressing roller 40 increases. For this reason, the contact areabetween the abutting portion 40 a and the side disk 12 b is reduced to acircle-like shape. In addition, the area of the torque transmissioncontact portion is also reduced to a circle-like shape. For this reason,the spin loss is reduced in the torque transmission contact portion.

As the thrust force increases, the second moment increases, and theinclination angle of the pressing roller 40 is reduced. As theinclination angle is reduced, a curvature of the abutting portion 40 aabutting on the side disk 12 b of the secondary disk 12 is reduced, andthe contact area between the pressing roller 40 and the side disk 12 bincreases. For this reason, it is possible to suppress an increase ofthe contact area and an increase of the pressure per unit area of thetorque transmission contact portion even when the thrust forceincreases. Therefore, it is possible to suppress deterioration of thepressing roller 40 or the disk.

(Shift Ratio Control)

Next, a description will be made for a shift ratio control using theelectric motor 34 with reference to the flowchart of FIG. 15.

In step S100, the ATCU 8 computes a vehicle speed based on a signal fromthe second rotation speed sensor 102.

In step S101, the ATCU 8 computes the input torque to the transmissionunit 3 based on a signal from the ECU.

In step S102, the ATCU 8 computes the target shift ratio using a mappreset based on the vehicle speed and the input torque.

In step S103, an actual shift ratio is computed based on a signal fromthe motor rotation sensor 100.

In step S104, the ATCU 8 computes a difference between the target shiftratio and the actual shift ratio.

In step S105, the ATCU 8 computes a movement amount of the pressingroller mechanism 30 corresponding to the difference, that is, the numberof steps corresponding to the manipulation amount of the electric motor34.

In step S106, the ATCU 8 controls the rotation of the rotation shaft ofthe electric motor 34 depending on the number of steps. When thedifference is a positive value, this means a downshift operation forchanging the shift ratio to the LOW side. Therefore, the electric motor34 moves the pressing roller mechanism 30 to the input shaft 10 side.When the difference is a negative value, this means an upshift operationfor changing the shift ratio to the HIGH side. Therefore, the electricmotor 34 moves the pressing roller mechanism 30 to the output shaft 14side. When the difference is zero, the shift operation is not performed.Therefore, the electric motor 34 holds the pressing roller mechanism 30in the current position. It is noted that an upper limit may be appliedto the number of steps.

Through the aforementioned control, the movement of the pressing rollermechanism 30 in parallel with the shaft center connecting line O iscontrolled, and the shift operation is executed depending on the targetshift ratio.

(Thrust Force Control)

A description will now be made for a thrust force control of theclamping force adjustment mechanism 32 with reference to the flowchartof FIG. 16.

In step S200, the ATCU 8 computes the target shift ratio. A method ofcomputing the target shift ratio is described in steps S100 to S102.

In step S201, the ATCU 8 computes the actual shift ratio based on thesignal from the motor rotation sensor 100.

In step S202, the ATCU 8 computes the difference between the targetshift ratio and the actual shift ratio.

In step S203, the ATCU 8 determines whether or not the difference iszero. If the difference is zero, the process advances to step S204. Ifthe difference is not zero, the process advances to step S205.

In step S204, the ATCU 8 sets a safety factor to “1.0.”

In step S205, the ATCU 8 sets the safety factor to “1.1.”

In step S206, the ATCU 8 computes the target slip rate. The slip rate isa ratio of the slip amount between primary disk 11 and the secondarydisk 12 relative to an input rotation speed. A description will now bemade for a target slip rate computation control with reference to FIG.17.

In step S300, the ATCU 8 computes an oil temperature of the oil suppliedto the transmission unit 3 based on a signal from the oil temperaturesensor.

In step S301, the ATCU 8 computes the target slip rate from the map ofFIG. 18 based on the oil temperature and the target shift ratio. Thetarget slip rate increases as the shift ratio is shifted to the LOWside, and the oil temperature increases.

FIG. 19 illustrates a relationship between the slip rate and the torquetransmission rate from the input shaft 10 to the output shaft 14. Asillustrated in FIG. 19, it is recognized that the torque transmissionrate from the input shaft 10 to the output shaft 14 is high when thereis a slight slip. This is because the transmission unit 3 transmits atorque from the input shaft 10 to the output shaft 14 by causing theprimary disk 11 and the secondary disk 12 to make contact with eachother to form the torque transmission contact portion, and a torque istransmitted in the torque transmission contact portion by causing theprimary disk 11 to drag the secondary disk 12. For this reason, in thetorque transmission contact portion, it is preferable to increase aratio of the area capable of transmitting a torque by generating a slipbetween the primary disk 11 and the secondary disk 12. In addition, itis recognized that the torque transmission rate increases when the sliprate is set to be high in the shift ratio closer to the LOW sidecompared to the HIGH side.

According to this embodiment, the target slip rate is preset such thatthe torque transmission rate increases based on FIG. 19, and thecomputation is performed based on the map of FIG. 18. In this manner,the target slip rate is computed. The target slip rate is set to a valuehigher than the torque transmission start slip rate of FIG. 19. Thetorque transmission start slip rate is a value at which a torque can betransmitted even when the shift ratio is at the lowest level.

Returning to FIG. 16, in step S207, the actual slip rate is computed.Here, a description will be made for a slip rate computation control forcomputing the actual slip rate with reference to the flowchart of FIG.20.

In step S400, the ATCU 8 computes the rotation speed of the output shaft14 based on a signal from the second rotation speed sensor 102.

In step S401, the ATCU 8 computes the rotation speed of the input shaft10 based on a signal from the first rotation speed sensor 101.

In step S402, the ATCU 8 computes the actual shift ratio based on asignal from the motor rotation sensor 100.

In step S403, the ATCU 8 computes the actual slip rate based on Equation(1).(Equation 1)Actual slip rate=((rotation speed of input shaft 10×actual shiftratio)−rotation speed of output shaft 14)/rotation speed of input shaft10  (1)

In this manner, the actual slip rate is computed.

Returning to FIG. 16, in step S208, the ATCU 8 computes the differencebetween the target slip rate and the actual slip rate as a slipdifference.

In step S209, the ATCU 8 determines whether or not the slip differenceis zero. If the slip difference is not zero, the process advances tostep S210. If the slip difference is zero, the process advances to stepS213.

In step S210, the ATCU 8 determines whether or not the slip differenceis greater than zero. If the slip difference is greater than zero, theprocess advances to step S211. If the slip difference is smaller thanzero, the process advances to step S212.

In step S211, the ATCU 8 sets a thrust force constant to “−Kp,” where“Kp” is a predetermined positive value.

In step S212, the ATCU 8 sets the thrust force constant to “Kp.”

In step S213, the ATCU 8 sets the thrust force constant to “0.”

In step S214, the ATCU 8 computes a target thrust force based on thefollowing Equation (2). It is noted that the target thrust force may becomputed based on the current turning angle of the second rollerfollower 79 and the actual shift ratio.(Equation 2)Target thrust force=(actual thrust force+thrust force constant)×safetyfactor  (2)

In step S214, the ATCU 8 computes the clamping force caused by theclamping force adjustment mechanism 32 based on the target thrust forceand the target shift ratio and computes the turning angle of the secondroller follower 79 that transmits the computed clamping force to theclamp arm 66.

In step S216, the ATCU 8 outputs the computed turning angle of thesecond roller follower 79 to the second actuator to turn the secondroller follower 79.

Through the aforementioned control, it is possible to control the sliprate to reduce the spin loss in the torque transmission contact portionand improve the torque transmission rate.

A description will now be made for the effects of the embodiments ofthis disclosure.

The pressing roller shaft 42 installed with the pressing roller 40extends to intersect with the shaft center connecting line O, one endside of the pressing roller shaft 42 is pivotably supported, and theclamping force is applied to the other end to generate the thrust forcein the pressing roller 40. Since the pressing roller shaft 42 is pivotedby using one end 42 a side as the fulcrum, it is possible to clamp theprimary disk 11 and the secondary disk 12 using a pair of pressingrollers 40 by applying a weak clamping force to a pair of pressingroller mechanisms 30 to form the torque transmission contact portion andtransmit rotation from the input shaft 10 to the output shaft 14. Inaddition, since it is possible to transmit rotation from the input shaft10 to the output shaft 14 by forming the torque transmission contactportion with a weak clamping force, it is possible to reduce a size ofthe transmission unit 3.

The clamp arm 66 is pivoted with respect to the shaft center of the armshaft 65 to clamp a pair of pressing roller shafts 42. Since the clamparm 66 is pivoted by using the arm shaft 65 as the fulcrum, it ispossible to clamp the end 42 b side of a pair of pressing roller shafts42 using a weak clamping force. For this reason, it is possible to clampthe primary disk 11 and the secondary disk 12 using a pair of pressingrollers 40 by applying a weak clamping force to form the torquetransmission contact portion and transmit rotation from the input shaft10 to the output shaft 14.

If the transmission unit 3 is seen from the axial direction of the inputshaft 10, a distance from the input shaft 10 to the torque transmissioncontact portion is equal to a distance from the shaft center of the armshaft 65 to a position where a pair of pressing roller shafts 42 areclamped by the clamp arm 66. As a result, it is possible to set a thrustforce under the same input torque of the input shaft 10 to a thrustforce matching the shift ratio and rapidly perform the shift operation.

The clamping force adjustment mechanism 32 is provided in the one end ofthe clamp arm 66 opposite to the arm shaft 65. It is possible to clampthe primary disk 11 and the secondary disk 12 using a pair of pressingrollers 40 using the clamp arm 66 by generating a weak clamping forceusing the clamping force adjustment mechanism 32 to form the torquetransmission contact portion and transmit rotation from the input shaft10 to the output shaft 14.

The clamping force adjustment mechanism 32 includes the pivot portion 73pivoted with respect to the shaft center of the second shaft portion 71connected to the rear clamp arm 68 and the curved portion 76 that isconnected to the end of the front clamp arm 67 and has the curvedsurface centered at the shaft center of the second shaft portion 71. Thepivot portion 73 has the second roller follower 79 that abuts and rollson the curved surface of the curved portion 76 so that the second rollerfollower 79 is biased to the second shaft portion 71 using thecompression spring 74. The clamping force adjustment mechanism 32 canchange the clamping force for clamping the pressing roller mechanism 30using the front and rear clamp arms 67 and 68 just by changing aposition of the second roller follower 79. It is possible to change thethrust force of the pressing roller 40 with a weak force and to reducethe size of the transmission unit 3 by reducing a size of the secondactuator for turning the second roller follower 79. In particular, byforming the curved surface in the arc shape, it is possible to turn thesecond roller follower 79 with a weak force.

Since the compression spring 74 is provided in the side opposite to thesecond roller follower 79 with respect to the second shaft portion 71,and the compression spring 74 is held in a compressed state, it ispossible to turn the second roller follower 79 without changing a springcompression amount of the compression spring 74. That is, since thesecond roller follower 79 can be turned without changing elastic energyof the compression spring 74, it is possible to turn the second rollerfollower 79 with a weak force. For this reason, it is possible torapidly turn the second roller follower 79 using a small-sized secondactuator and reduce the size of the transmission unit 3 by reducing thesize of the second actuator.

By arranging the second roller follower 79 in the vicinity of thereference position, it is possible to set the clamping force of theclamp arm 66 to an insignificant value or zero and prevent formation ofthe torque transmission contact portion. As a result, it is possible toeasily perform the downshift control.

By turning the second roller follower 79 such that the turning angle isreduced from the reference position, it is possible to lengthen thedistance between the clamp arms 66 and further reduce the clamping forceof the clamp arm 66. As a result, it is possible to reliably prevent theprimary disk 11 and the secondary disk 12 from making contact with eachother and forming the torque transmission contact portion.

When the gap is not provided between the arm shaft 65 and the clamp arm66 and between the second shaft portion 71 and the pivot portion 73, itmay be difficult to clamp a pair of pressing roller mechanisms 30 usingthe clamp arm 66 with excellent balance due to a dimensional tolerance,a component variation, and the like. For this reason, for example, athrust force of one of the pressing rollers 40 becomes smaller than athrust force of the other pressing roller 40. As a result, it may bedifficult to transmit rotation from the primary disk 11 to the secondarydisk 12 in the pressing roller 40 side having a smaller thrust force. Inaddition, a load applied to the pressing roller mechanism 30 having alarger thrust force increases so that the pressing roller mechanism 30may be deteriorated. In order to prevent such deterioration, a componenthaving a higher strength may be employed. However, this may increasecost. According to this embodiment, by providing the gap between thesecond shaft portion 71 and the casing 70 even when there is thedimensional tolerance, the component variation, and the like. Therefore,by absorbing such influence using the gap, it is possible to clamp apair of pressing roller mechanisms 30 using the clamp arm 66 withexcellent balance. For this reason, it is possible to transmit thethrust force to the primary disk 11 and the secondary disk 12 using thepressing roller 40 with excellent balance and suppress deterioration ofthe pressing roller mechanism 30 and the cost increase.

The pressing roller shaft 42 is supported by the first and secondsupport portions 43 and 44 tiltably in the shaft center connecting lineO direction, and the second support portion 44 is located in theupstream side from the pressing roller 40 in the rotation direction ofthe primary disk 11. In addition, the shift operation is performed bymoving the second support portion 44 along the shaft center connectingline O using the first actuator 33. As a result, when the pressingroller shaft 42 and the pressing roller 40 are inclined as the secondsupport portion 44 moves during the shift, the force following themovement of the second support portion 44 is generated from the pressingroller 40 itself. For this reason, it is possible to move the pressingroller 40 along the shaft center connecting line O to perform the shiftoperation by applying a weak force to the second support portion 44using the first actuator 33. Furthermore, since the force that followsmovement of the second support portion 44 is generated in the pressingroller 40 itself, it is possible to rapidly perform the shift operation.

Even when the pressing roller shaft 42 is tilted while no shiftoperation is performed, it is possible to return the pressing roller 40and the pressing roller shaft 42 to their original positions by virtueof the force generated in the pressing roller 40.

Since the pressing roller 40 is inclined to the output shaft 14 side, itis possible to reduce the spin loss between the pressing roller 40 andthe side disk 12 b of the secondary disk 12 and increase a torquetransmission rate from the input shaft 10 to the output shaft 14. Inparticular, when the shaft center of the pressing roller 40 intersectswith the rotation center P on the surface of the side disk 12 b, it ispossible to reduce the spin loss between the pressing roller 40 and theside disk 12 b.

It is possible to change the inclination angle of the pressing roller40, the curvature of the curved surface where the abutting portion 40 aof the pressing roller 40 abuts on the side disk 12 b of the secondarydisk 12, and the shape and the area of the torque transmission contactportion depending on the thrust force of the pressing roller 40. Whenthe thrust force of the pressing roller 40 is large, it is possible tosuppress deterioration of the primary disk 11, the secondary disk 12, orthe pressing roller mechanism 30 by causing the curved surface having asmall curvature to abut on the side disk 12 b to increase the area ofthe torque transmission contact portion. Furthermore, when the thrustforce of the pressing roller 40 is small, it is possible to reduce thearea of the torque transmission contact portion to reduce the spin lossin the torque transmission contact portion by causing the curved surfacehaving a large curvature to abut on the side disk 12 b and making theshape of the torque transmission contact portion in the circle-likeshape.

In the pressing roller 40, the first moment is generated by the biasingportion 45, and the second moment opposite to the first moment isgenerated by the reactive force from the disks 11 and 12 in response tothe thrust force of the pressing roller 40. The pressing roller 40 isinclined such that both moments are balanced, and the pressing roller 40is held in this position. That is, it is possible to automaticallychange the shape and the area of the torque transmission contact portiondepending on the thrust force of the pressing roller 40. It is possibleto suitably change the shape and the area of the torque transmissioncontact portion without controlling with a new actuator.

It is possible to improve the torque transmission rate by computing thetarget slip rate which is higher than the torque transmission start sliprate at which a torque can be transmitted from the primary disk 11 tothe secondary disk 12 and controlling the thrust force of the pressingroller 40 using the clamping force adjustment mechanism 32 such that theslip rate in the torque transmission contact portion reaches the targetslip rate. It is possible to improve the torque transmission rate byincreasing the target slip rate as much as the shift ratio is lowered.

The primary disk and the secondary disk are the plate-like member havinga thin thickness. The primary disk and the secondary disk may not makecontact depending on a component variation when they are clamped andpressed by the pressing rollers.

According to this embodiment, by setting the thickness of the centerdisk 12 a of the secondary disk 12 positioned in the center of the axialdirection of the input shaft 10 to be thicker than the thicknesses ofother disks, it is possible to cause the secondary disk 12 and theprimary disk 11 to reliably make contact with each other when the torquetransmission contact portion is formed by the pressing roller 40.Therefore, it is possible to improve the torque transmission rate.

Since the side disk 12 b is warped to the side opposite to the centerdisk 12 a toward the outer radial direction, it is possible to suppresscontact between the side disk 12 b and the primary disk 11 in the areasother than the torque transmission contact portion by forming a gapbetween the side disk 12 b and the primary disk 11 without providing athrust ball bearing.

By changing the lock/unlock state of the dry starter clutch 15 using thefirst actuator 33 that shifts the pressing roller mechanism 30 in theshaft center connecting line O direction, it is possible to change thelock/unlock state of the dry starter clutch 15 and perform the shiftoperation of the transmission unit 3 using a single actuator. Therefore,it is possible to reduce the number of actuators and cost. Accordingly,it is possible to reduce a size of the vehicle automatic transmissionsystem 1.

The tapered surface 37 a is provided in the bracket 37 that moves in theshaft center connecting line O direction using the electric motor 34,and the lock/unlock state of the dry starter clutch 15 is changed byshifting the pushrod in the axial direction of the input shaft 10 alongthe tapered surface 37 a. Using such a simple and easy configuration, itis possible to change the lock/unlock state of the dry starter clutch15.

When the vehicle is parked by manipulating the selector to theP-position, the reverse gear 16 is engaged with the input shaft 10, andthe primary disk 11 and the secondary disk 12 are clamped and pressed bythe pressing rollers 40 to form the torque transmission contact portion.As a result, it is possible to prevent movement of the vehicle byinterlocking the transmission unit 3.

According to this embodiment, the gap is formed between the pressingroller shaft 42 and the first support portion 43, and the end of thepressing roller shaft 42 supported in the second support portion 44 sidehas the spherical shape. However, any configuration may be employedwithout limiting thereto if the pressing roller shaft 42 and thepressing roller 40 can be tilted in the shaft center connecting line Odirection. For example, a gap may be formed between the pressing rollershaft 42 and the second support portion 44.

Although the gap is provided between the second shaft portion 71 and thecasing 70 in this embodiment, a gap may be provided between the armshaft 65 and the clamp arm 66.

Although the torque transmission contact portion is not formed in thereference position in this embodiment, the torque transmission contactportion may not be formed in a position where the second roller follower79 is turned to the front clamp arm 67 side from the reference position.

The target slip rate may be set to be higher at a slow vehicle speedrather than a fast vehicle speed. In addition, the target slip rate maybe set to be higher as the accelerator opening level increases, or theaccelerator pedaling amount per unit time increases.

Although the center disk 12 a is provided in the secondary disk 12 inthis embodiment, the center disk 12 a may be provided in the primarydisk 11.

The outer circumferential edge side of the primary disk 11 may be warpedtoward the center disk 12 a side of the secondary disk 12. As a result,it is possible to further suppress the contact between the side disk 12b and the primary disk 11 in the area other than the torque transmissioncontact portion between the side disk 12 b and the primary disk 11.

Although the pressing roller 40 is inclined to the output shaft 14 sidein this embodiment, the pressing roller 40 may be inclined to the inputshaft 10 side.

Although various embodiments of this disclosure have been describedhereinbefore, they are just for illustrative purposes and are notintended to specifically limit the technical scope of the invention.Instead, it would be appreciated that that various changes ormodifications may be possible without departing from the spirit andscope of the invention.

The invention claimed is:
 1. A continuously variable transmissioncomprising: an input shaft connected to a motor and supported by atransmission unit casing member; an output shaft arranged in parallelwith the input shaft and supported by the transmission unit casingmember; a discoidal input disk that is provided in the input shaft andhas an outer circumferential edge arranged close to the output shaft; adiscoidal output disk that is provided in the output shaft and has anouter circumferential edge arranged close to the input shaft; a pair ofpressing units provided movably along a shaft center connecting lineobtained by connecting a shaft center of the input shaft and a shaftcenter of the output shaft in a disk overlapping area where the inputdisk and the output disk are overlapped, so that a torque transmissioncontact portion is formed by clamping and pressing both the disks in aposition corresponding to a target shift ratio to elastically deformboth the disks; a target slip rate setting unit that is configured toset a target slip rate between the input disk and the output disk in thetorque transmission contact portion to a value higher than a torquetransmission start slip rate in the torque transmission contact portion;and a control unit that is configured to control a force for clampingand pressing both the disks using the pressing units such that an actualslip rate in the torque transmission contact portion becomes the targetslip rate.
 2. The continuously variable transmission according to claim1, wherein the control unit is configured to reduce the force forclamping and pressing the disks as the target slip rate increases. 3.The continuously variable transmission according to claim 1, wherein thetarget slip rate increases as a shift ratio is set to a lower position.4. A control method for continuously variable transmission having: aninput shaft connected to a motor and supported by a transmission unitcasing member; an output shaft arranged in parallel with the input shaftand supported by the transmission unit casing member; a discoidal inputdisk that is provided in the input shaft and has an outercircumferential edge arranged close to the output shaft; a discoidaloutput disk that is provided in the output shaft and has an outercircumferential edge arranged close to the input shaft; and a pair ofpressing units provided movably along a shaft center connecting lineobtained by connecting a shaft center of the input shaft and a shaftcenter of the output shaft in a disk overlapping area where the inputdisk and the output disk are overlapped, so that a torque transmissioncontact portion is formed by clamping and pressing both the disks in aposition corresponding to a target shift ratio to elastically deformboth the disks, the control method comprising: setting a target sliprate between the input disk and the output disk in the torquetransmission contact portion to a value higher than a torquetransmission start slip rate in the torque transmission contact portion;and controlling a force for clamping and pressing both the disks usingthe pressing units such that an actual slip rate in the torquetransmission contact portion becomes the target slip rate.
 5. Thecontrol method for continuously variable transmission according to claim4, wherein the force for clamping and pressing the disks is reduced asthe target slip rate increases.
 6. The control method for continuouslyvariable transmission according to claim 4, wherein the target slip rateincreases as a shift ratio is set to a lower position.
 7. A continuouslyvariable transmission comprising: an input shaft connected to a motorand supported by a transmission unit casing member; an output shaftarranged in parallel with the input shaft and supported by thetransmission unit casing member; a discoidal input disk that is providedin the input shaft and has an outer circumferential edge arranged closeto the output shaft; a discoidal output disk that is provided in theoutput shaft and has an outer circumferential edge arranged close to theinput shaft; a pair of pressing units provided movably along a shaftcenter connecting line obtained by connecting a shaft center of theinput shaft and a shaft center of the output shaft in a disk overlappingarea where the input disk and the output disk are overlapped, so that atorque transmission contact portion is formed by clamping and pressingboth the disks in a position corresponding to a target shift ratio toelastically deform both the disks; target slip rate setting means forsetting a target slip rate between the input disk and the output disk inthe torque transmission contact portion to a value higher than a torquetransmission start slip rate in the torque transmission contact portion;and control means for controlling a force for clamping and pressing boththe disks using the pressing unit such that an actual slip rate in thetorque transmission contact portion becomes the target slip rate.
 8. Thecontinuously variable transmission according to claim 7, wherein thecontrol means is configured to reduce the force for clamping andpressing the disks as the target slip rate increases.
 9. Thecontinuously variable transmission according to claim 7, wherein thetarget slip rate increases as a shift ratio is set to a lower position.